Type I collagen fibrils form the principal structural elements of most connective tissues and determine their physical properties. A long term objective of this project has been to understand the basic events involved in the fibril assembly and organization processes. A second goal has been to delineate the details of the assembly of procollagen molecules from their individual pro alpha-chains and to determine the factors which regulate chain selection and registration. To achieve these objectives three specific studies are proposed. 1. The cotranslational processing and assembly of procollagen molecules. Nascent pro alpha-chains reside on complex polyribosomal aggregates and elongate with synthesis pauses. The nascent chains will be analyzed to determine pause loci and their relation to specific sequence, cotranslational modification, and chain association requirements. The role of the polysome aggregate in chain selection and registration will be studied as related to cytosolic, membrane protein, and intrinsic mRNA factors. Chick tendon fibroblasts, and 2 cell lines which produce only pro alpha 1- and pro alpha 2-chains, respectively, will be studied by biochemical an electron microscopic techniques. 2. The assembly of monomeric collagen into fibrils. D-periodic assembly is dominated by telopeptide-helix receptor interactions which may involve subtle conformational alterations in both domains. These will be examined by FTIR spectroscopy and other physical techniques during the fibril formation process. Intact and specific atelopeptide collagens, and synthetic telopeptide and helix region sequence models for the interaction systems will be studied. 3. The development of fibril organization. Collagen-interacting macromolecules of the extracellular matrix affect fibril architecture and organization. A theoretical framework for considering these interactions has been constructed and will guide EM studies examination of the effects of specific matrix polyanionic components on fibril organization. These studies all have the ultimate objective of providing insight into the nature of connective tissue dysfunctions.